This invention generally relates to an irrigation system and a drive unit for use therewith, and more specifically relates to a continuous move side roll irrigation system and a drive unit therefor. Such systems are of a type including a conduit which extends across the area to be irrigated. Such a conduit can be several hundred feet long. The conduit is supported above the ground by a series of spaced concentric wheels which are secured to the conduit for rotation therewith, and a series of sprinklers are spaced along the conduit for delivering liquid fed through the conduit to the area to be irrigated. The conduit is made to travel more or less continuously in a linear movement over the field by imparting rotation to the conduit and thereby imparting rotation to the wheels supported thereon.
Such side rolls systems are known in the art and are used with a drive unit which functions both to rotatably drive the conduit and supply liquid to the conduit as it is caused to move over the area to be irrigated. Such drive units are also generally known in the art. An example is shown in U.S. Pat. No. 3,848,625.
However, certain problems have been associated with these side roll and drive unit systems due to the difficulty of maintaining proper alignment of the drive unit relative to the conduit and of maintaining a selected speed. It is customary in these systems for the liquid to be supplied to the conduit by means of a hose which is dragged along by the drive unit, the other end of the hose being connected to a suitable supply of liquid. Since the amount of liquid which must be supplied to the conduit is relatively large, the conduit being as much as 4 to 7 inches in diameter, the size and weight of the hose that must be pulled along by the drive unit are substantial, and thus the drive unit must also include some means for driving the drive unit as well as rotatably driving the conduit. Heretofore it has been customary to drive the drive unit along the path and rotatably drive the conduit at predetermined fixed speeds. However, this approach has not been totally satisfactory for the following reasons:
As the drive unit and conduit move over the field, the topography of the land over which the conduit moves may be and usually is different from that over which the drive unit moves. Thus, the distance that the drive unit moves from one end of the field to the other is likely to be different from the distances traveled by the conduit wheels due to hills and depressions over which the wheels must roll. If the relative speed between the drive unit and conduit is fixed, there is no compensation for these differences in the distances travelled with the result that the drive unit will move ahead or behind the conduit causing misalignment. If this misalignment becomes excessive, the conduit can rupture resulting in costly shutdown and repair.
Another problem that occurs is that as the drive unit and conduit move down the field, the amount and therefore weight of hose that is dragged by the drive unit, together with the weight of the water in the hose, continually increases. This places a continually increasing load on the drive unit. As the load increases, the speed of the drive unit decreases and if the relative speed of the drive unit and conduit is fixed, the speed of the conduit also decreases. Not only does this slow down the irrigation process, but it also produces an uneven amount of irrigation over the field.
The system and control unit of this invention overcome these problems by automatically regulating the relative speed of the drive unit and the conduit in response to fore and aft displacement of the drive unit relative to the conduit. In a preferred embodiment of the invention, the speed of the drive unit is varied to maintain alignment with the conduit so that there is no rupturing of the conduit due to misalignment and no slowdown of the drive unit and conduit due to an increasing load placed on the drive unit by the hose.
Generally, the drive unit in the system of this invention includes a frame with wheels rotatably mounted to the frame for supporting the frame above the ground and for moving it along a path. The conduit of the irrigation system is rotatably mounted to the frame and there is included in the drive unit a means for rotatably driving the conduit thereby imparting rotation to the wheels upon which the conduit is supported. The drive unit also includes means for supplying liquid to the conduit for continuously applying the liquid to the field over which the conduit moves.
A cable gripping device is provided as part of the drive unit and engages a fixed cable stretched along the path for the drive unit. Means are provided for operating the cable gripping device thereby moving the drive unit along the fixed cable.
A linkage arrangement is connected between the conduit and the drive unit, portions of which extend from the conduit at angles toward the drive unit. The linkage is part of a control system for controlling the speed of operation of the cable gripping device relative to the speed of rotation of the conduit in response to movement of the linkage corresponding to fore and aft displacement of the drive unit relative to the conduit.
In a preferred embodiment of the invention, the drive means for the cable gripping device and conduit are liquid powered with the speed of these drives being proportional to the amount of liquid supplied to the liquid power sources. The control means includes means for varying the amount of liquid supplied to the liquid power source in response to fore and aft displacement of the drive unit relative to the conduit.
Means are also provided for shutting off the water to the system, thus deactivating both drive means at predetermined displacements of the drive unit relative to the conduit.
Thus, it is a primary object of this invention to provide an irrigation system and drive unit therefor wherein the relative speed of the drive unit and the conduit is automatically controlled, and further where this control is in response to relative displacement of the drive unit and conduit. These and other objects of the invention are apparent from the drawing and detailed description to follow.